Grade braking in passenger vehicles has been left to the purview of the operator of the vehicle. If the operator wishes the vehicle to decelerate or have a constant speed on a down grade, the brake pedal is depressed in an effort to slow the vehicle. Many drivers recognize that, with automatic transmissions, it is possible to control the down grade speed somewhat by shifting the transmission to a lower drive ratio (fourth to third, or fourth to third to second) and employing the brakes simultaneously. As with manual or countershaft type transmissions, this requires a manual input or shift effort from the operator.
In some instances, the operator may be slow to recognize the increasing speed rate of the vehicle. Under these conditions, the brake application pressure must be increased. While this maintains the vehicle speed in a range that the operator finds comfortable, the brake wear, lining and rotor temperature and the amount of brake fade increase. This can have a shortening effect on the life of the brakes which will require the vehicle owner to replace or service the brakes more often.
With the advent of electro-hydraulic controls, many additional automatic functions can be made available to the operator and transmission control becomes more precise. Ratio interchanges are considerably improve with the use of lookup tables to determine the shift sequence and timing. The widespread introduction of anti-lock braking systems has also improved the vehicle braking function.